Regardless of whether Republicans wrest control of the Senate from Democrats Tuesday night, the institution will have at least a short-term knowledge gap on military matters next year after a bevy of defense-savvy senators retire.

Seven senators who regularly delve into Pentagon budgeting and weapon-systems debates–including Sens. Joe Lieberman (I/D-Conn.) and Jon Kyl (R-Ariz.)–are due to retire in January. In addition, several prominent Senate Armed Services Committee (SASC) members face tough challengers during tonight’s election, including Pentagon-contracting watchdog Sen. Claire McCaskill (D-Mo.) and the pro-military Sen. Scott Brown (R-Mass.).

Recent polls suggest McCaskill may triumph over challenger Rep. Todd Akin (R-Mo.), who stirred a national controversy over comments on rape. Akin is currently chairman of the House Armed Services Committee’s (HASC) Seapower and Projection Forces subcommittee. Brown is facing a very close fight against Harvard Law School professor Elizabeth Warren, and contradictory polls in recent days show both Brown and Warren winning, indicating the final vote tally will be close.

Many of the definitely or potentially departing defense-minded senators are in the Democratic party, which controls the Senate with 53 seats, including two independents, compared to Republicans’ 47 spots. While Republicans could in theory seize control of the body at the polls tonight, prominent pollsters including Stuart Rothenberg in recent days predicted Democrats will retain control.

Thus, losing people like the retiring Ben Nelson (D-Neb.), chairman of the SASC’s Strategic Forces subcommittee, will create notable gaps in full-and-sub-committee leadership spots as the next session of Congress starts in 2013, pundits said.

“The loss of so many defense-savvy senators will create a knowledge gap,” Travis Sharp, a defense budget expert and fellow at the Center for a New American Security (CNAS) think tank in Washington, told Defense Daily.

However, Sharp cautioned against assuming there will be a significant and lasting void in military aptitude, considering defense-related committees “are filled with senators whose constituents depend on defense dollars, and there is no shortage of senators who fit that description and thus have a political incentive to become defense experts in order to bring home the bacon.”

“Since defense will continue to matter to communities across the country, we will always have a large number of senators who will take an active interest in military matters, particularly as veterans of the wars in Iraq and Afghanistan begin to enter public office,” Sharp said.

Mackenzie Eaglen, a fellow at the conservative American Enterprise Institute think tank, similarly said the “loss of so many esteemed veterans of defense and military issues will have a noticeable impact on the committees of jurisdiction at a programmatic level.”

Still, Eaglen told Defense Daily she expected the Senate’s interest in “detailed and robust oversight of weapons programs” to continue, calling it a “priority issue now ingrained into every member, new and old” on the SASC.

She further noted the big-picture debate over the defense budget is largely controlled by the president and congressional leadership.

In January three of the SASC’s six subcommittee chairs will retire: Lieberman, chairman of the Air Land subpanel that oversees programs including the F-35 Joint Strike Fighter, who fights for home state contractors including Pratt & Whitney [UTX]; Nelson, head of the Strategic Forces subcommittee that authorizes missile-defense programs and also a member of the powerful, budget-dictating Senate Appropriations Committee (SAC); and Sen. Jim Webb (D-Va.), chair of the Personnel subpanel and a former Navy secretary with a strong voice in naval shipbuilding matters. SASC member Daniel Akaka (D-Hawaii), who has joined in shipbuilding debates and chairs the Senate Homeland Security and Government Affairs Committee’s Oversight of Government Management subcommittee, also is leaving the Senate.

Sen. Kay Bailey Hutchison, a member of the SAC’s Defense subcommittee who advocates regularly for Lockheed Martin [LMT] programs like the F-35, is due to retire. Also leaving are two prominent voices in Senate-wide defense-budgeting debates: Kyl, the Senate minority whip and staunch Pentagon budget and missile-defense booster, and Sen. Olympia Snowe, a touter of shipbuilding efforts that benefit General Dynamics [GD] Bath Iron Works and Portsmouth Naval Shipyard.

These departing senators hold additional committee posts key to the defense-aerospace committee. For example, Lieberman chairs the Homeland Security and Government Affairs Committee, which oversees Department of Homeland Security and cyber-security. Hutchison is ranking member of the Senate Commerce, Science, and Transportation Committee, which oversees NASA programs that she has monitored very closely.

Sharp, for one, isn’t worried about those senators’ states being left with Pentagon-oversight neophytes.

“The next senators from Connecticut, Virginia, Texas, Maine, and Hawaii will all become knowledgeable about defense because defense is huge in those states, and thus they have to be military-savvy to keep their jobs,” he said.

In the House–which pundits predict will remain in Republican control after the election–a slew of notable defense-watchdogs are moving around as well. Retirees include Rep. Norm Dicks (D-Wash.), an unabashed Boeing [BA] supporter who is ranking member of the all-powerful House Appropriations Committee and its defense subcommittee.

Rep. Roscoe Bartlett (R-Md.) may lose his seat, representing a recently-reconfigured district, thus also vacating his position as chairman of the HASC’s Tactical Air and Land Forces subcommittee. Other HASC members facing challenging opponents include Rep. Mike McIntyre (D-N.C.), ranking member on the Seapower and Projection Forces subcommittee, and Reps. Allen West (R-Fla.), Mark Critz (D-Pa.), and Larry Kissell (D-N.C.).